We studied thyroid abnormalities in 50 patients with dermatitis herpetiformis. Two patients had a history of hyperthyroidism, and 5 had hypothyroidism and were on thyroid replacement therapy. Three patients had had thyroidectomies for nodules, and 5 had asymptomatic goiter. Two patients were clinically euthyroid with elevated thyrotrophin and low normal thyroxine levels, indicating early thyroid insufficiency. Thyroid microsomal antibodies were seen in 38% of patients with dermatitis herpetiformis compared to 12% of controls. The presence of clinical or serologic thyroid abnormalities in 26 of 50 patients shows a significant but unexplained association between dermatitis herpetiformis and thyroid disease.